66 PHYSIOLOGY OF STREAMING MOVEMENTS 



suddenly raised to 60 C. streaming ceases within two minutes, and if 

 immediately returned to 25 C. does not recommence until after fifteen 

 minutes to five hours. The direction of streaming is occasionally reversed 

 in cells bordering on ones which have been killed by the exposure l . 



SECTION 26. Effect of Sudden Changes of Temperature. 



According to both Dutrochet (I.e.) and Hofmeister 2 , a sudden and 

 pronounced change of temperature may act as a stimulus temporarily 

 inhibiting or retarding streaming in Chara and Nitclla. Velten 3 ex- 

 pressly denies this, but Hermann 4 was able in part to confirm the older 

 observations. According to this author, a marked and sudden fall of 

 temperature always causes a temporary stoppage, although a sudden 

 rise of temperature, if below 45 C., always produces an acceleration, 

 whereas above 45 C. retardation may ensue. Localized cold applied to 

 one end of a warm cell of Nitella causes an almost immediate stoppage 

 of streaming, and similarly, if a cell at 5 C. has one end suddenly warmed 

 to 30 C., streaming also ceases after a latent period of ten to thirty seconds. 

 In this latter case the stoppage is also due to a.'fall of temperature and 

 occurs when the protoplasm warmed at one end is cooled by streaming 

 into the cold part of the cell, the long latent period representing mainly 

 the time of streaming past the warm end. 



The above action is that of a shock-stimulus producing a temporary 

 disturbance of the motor-mechanism. When different regions of a cell are 

 kept at different temperatures, streaming is slower, and the stream thicker, 

 over the cold region than over the warm one. Thus, with one half at 

 4 C. and the other at i6C., streaming may be more than twice as rapid 

 in the second half than in the first. The relative viscosities of albumin at 

 these temperatures are as 10 : 7, so that a large part of the difference of 

 velocity is probably due to the different viscosities of the streaming plasma 

 in the warm and cold halves of the cell. A difference of temperature of 

 25 C. to 35 C. (2C. at one end, 37 C. at the other) soon causes pro- 

 nounced aggregation and death in two to three hours. Hermann denies 

 that a sudden rise of temperature ever causes a stoppage unless the 

 maximal point is reached or passed. Klemm 5 has, however, shown that 

 when hairs of Momordica are suddenly raised from i8C. to 45 C. stream- 

 ing ceases momentarily, is then resumed again, and ultimately ceases. The 

 same is the case when cells of Nitella and Chara are suddenly raised from 



Streaming takes place normally in opposite directions on the two sides of each dividing wall. 



Die Lehre von der Pflanzenzelle, 1867, p. 53. 



Flora, 1876, p. 214. 



Protoplasmastromung bei den Characeen, Jena, 1898, p. 44. 



Jahrb. f. wiss. Hot, Bd. xxvni, p. 15 ; cf. also Sachs, Flora, 1864, p. 65. 



